<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Title</title>
  <style>
    .container {
      height: 1000px;
      background-color: #f40;
    }

    @media (min-width: 768px) {
      /*条件满足时才会执行*/
      .container {
        width: 750px;
      }
    }

    @media (min-width: 992px) {
      /*条件满足时才会执行*/
      .container {
        width: 972px;
      }
    }

    @media (min-width: 1200px) {
      /*条件满足时才会执行*/
      .container {
        width: 1000px;
      }
    }
  </style>
</head>
<body>
<div class="container"></div>
</body>
</html>